1. Field of the Invention
The present invention relates to a solid-state imaging apparatus used for a digital video camera, a digital still camera and an image input apparatus such as an image scanner.
2. Description of the Related Art
In a solid-state imaging apparatus, an increase in speed of readout is requested. There is a technique disclosed in Japanese Patent Application Laid-Open No. 2001-45378 in response to this request. In the technique disclosed in Japanese Patent Application Laid-Open No. 2001-45378, in a pixel array in which plural pixels are arrayed in a matrix form, a signal for driving the pixels is supplied to the pixels in the same row and signals of the pixels are read out via plural column signal lines extending in a direction along columns. Holding units for holding the signals from the pixels are respectively connected to one end and the other end of each of the column signal lines. In parallel to operation for reading out a signal held by one of the two holding units connected to one column signal line, operation for holding a signal output from the pixels in the other holding unit is performed. This can reduce a blanking period, which is a period in which no sensor output is performed, and reduce a readout period.
As another method of realizing an increase in speed of readout, a technique called thinning-out, addition, or averaging, are known. These techniques are often used for an application such as a moving image that is not required of resolution as high as that of a still image. The thinning-out is a technique for forming an image using only signals from pixels in a part of a pixel array. On the other hand, the addition or averaging is a technique for adding or averaging signals from plural pixels. When an increase in speed is realized by the thinning-out, signals are lost and resolution falls. Therefore, when a subject oblique to a matrix of a pixel array is photographed, a step-like image called jaggy may be formed. On the other hand, when the addition or averaging is performed, jaggy can be reduced because signals are not lost. In Japanese Patent Application Laid-Open No. 2004-304771, signals from plural pixels connected to the same column signal line are averaged.
However, in Japanese Patent Application Laid-Open No. 2001-45378, considering that resolution falls when signals are added, the addition or averaging is not examined.
In Japanese Patent Application Laid-Open No. 2004-304771, after signals of pixels to be averaged are held by different capacitors, respectively, the capacitors are electrically connected to read out an averaged signal. An increase in speed of readout is not examined.